Which of the following activities is most likely to improve muscular endurance? A. high jumping B. long distance running C. sprinting D. throwing a fast ball

The correct answer should probably be B. Long distance running. To increase endurance you have to expose yourself to longer physical activities, usually of the cardio type. Based on that, long distance running is here the only option that fits because all others are short and brief and don't increase your muscle strength and endurance in the long run.